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Showing papers in "Journal of Porous Materials in 2003"


Journal ArticleDOI
TL;DR: In this paper, the synthesis and absorbing properties of a wide variety of porous sorbent materials have been studied for application in the removal of organics, particularly in the area of oil spill cleanup.
Abstract: This paper reviews the synthesis and the absorbing properties of the wide variety of porous sorbent materials that have been studied for application in the removal of organics, particularly in the area of oil spill cleanup. The discussion is especially focused on hydrophobic silica aerogels, zeolites, organoclays and natural sorbents many of which have been demonstrated to exhibit (or show potential to exhibit) excellent oil absorption properties. The areas for further development of some of these materials are identified.

987 citations


Journal ArticleDOI
TL;DR: In this article, both carbon fibre reinforced and polymeric bound aerogel electrodes based on polytetrafluoroethylene (PTFE) have been investigated with respect to their electrical conductivity, surface area and capacitive performance.
Abstract: Carbon aerogels are prepared here via pyrolysis of resorcinol-formaldehyde aerogels. Their open porous and electrically conductive structure renders carbon aerogels suitable for the application in supercapacitors. Different types of electrodes can be derived from the sol-gel-precursors of carbon aerogels: Monolithic fibre-reinforced electrodes and polymer-carbon compounds. Both carbon fibre reinforced and polymeric bound aerogel electrodes based on polytetrafluoroethylene (PTFE) have been investigated in this work with respect to their electrical conductivity, surface area and capacitive performance. The capacitance of both electrode types is above 65 F/cm3 in aqueous electrolytes and this meets the demands of supercapacitor electrodes.

124 citations


Journal ArticleDOI
TL;DR: In this article, a series of acetic acid catalyzed carbon aerogels with different dilutions of the catalyst and the monomers were investigated accurately, and the connectivity of the primary particles turned out to be exceptionally high, as was found from SEM photographs.
Abstract: We prepared carbon aerogels with a wide range of structural properties and densities using the weak acetic acid as a catalyst. Two series of acetic acid catalyzed carbon aerogels with different dilution of the catalyst and the monomers were investigated accurately. Structural investigation was performed via (U)SAXS, gas sorption and SEM. The pore and particle size can be tailored according to the used amount of monomers and catalyst, respectively. The connectivity of the primary particles turned out to be exceptionally high, as was found from SEM photographs and is reflected in a large elastic modulus and a high electrical conductivity. IR transmission spectra of the acetic acid catalyzed resorcinol-formaldehyde aerogels indicate the existence of a carbonyl group within the aerogel network, which may be important for the structural development of the this gel. As no metal containing catalyst was employed, the resulting carbon aerogels are extremely pure.

63 citations


Journal ArticleDOI
TL;DR: In this paper, a process for the production of SiOC ceramic foams has been developed through melt foaming of a siloxane preceramic polymer with the help of a blowing agent, followed by pyrolysis under an inert atmosphere.
Abstract: A process for the production of SiOC ceramic foams has been for the first time developed through melt foaming of a siloxane preceramic polymer with the help of a blowing agent, followed by pyrolysis under an inert atmosphere. The raw material consisted of a methylsilicone resin, a catalyst (which accelerated the cross-linking reaction of the silicone resin) and a blowing agent (which generated gas above 210°C). Methylsilicone resin foams were obtained through controlling the melt viscosity around 210°C, temperature where the blowing agent started to decompose, by varying the initial molecular weight of the preceramic polymer and the amount of the catalyst. The obtained SiOC ceramic foams exhibited excellent oxidation stability up to 1000°C, as shown by thermal gravimetric analysis (TGA). As expected, the mechanical properties of the SiOC ceramic foams varied as a function of their bulk density, possessing a flexural strength up to 5.5 MPa and a compression strength up to 4.5 MPa. The main steps in the process, namely foaming and pyrolysis, were analyzed in detail. The viscosity change was analyzed as a function of temperature by the dynamic shear measurement method. The pyrolysis process of foams was analyzed by TGA coupled with infrared spectroscopy (IR).

41 citations


Journal ArticleDOI
TL;DR: In this article, three types of layered silicates, namely octosilicate, magadiite and kenyaite, were synthesized using poly(ethylene glycol) (PEG).
Abstract: Three types of layered silicates, namely octosilicate, magadiite and kenyaite, were synthesized using poly(ethylene glycol) (PEG). The influence of reaction parameters, including alkali source, silica source, PEG molecular weight, reaction time and temperature, on the formation of these three phases was investigated. The results indicate that magadiite is preferred when (i) using NaOH as the alkali source and at a lower temperature (150°C), with fumed silica, tetramethyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS), Ludox-AS 40 or colloidal sol acting as the silica source in the presence of PEG 200; (ii) using fumed silica as the silica source and PEG 300 as the template at 150°C; (iii) at a higher temperature (180°C), using PEG 200 as template and TEOS as the silica source; and (iv) at 180°C with a combination of PEG 300 and fumed silica. Compared to magadiite, kenyaite was favored at a higher temperature (180°C) with PEG 200 and NaOH, KOH or RbOH, while using fumed silica, silica gel, or colloidal sol as silica source; or at the lower temperature (150°C) using NaOH as alkali source, PEG 200 as template, and silica gel or silicic acid as the silica source. Octosilicate was obtained at 90°C with the combination of NaOH, PEG 200 and fumed silica.

36 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of adding trimethylethoxysilane (TMES) as a co-precursor on the hydrophobicity and physical properties of tetraethoxysilicane (TEOS) based silica aerogels is reported.
Abstract: The experimental results on the effect of adding trimethylethoxysilane (TMES) as a co-precursor on the hydrophobicity and physical properties of tetraethoxysilane (TEOS) based silica aerogels, are reported. The molar ratio of TEOS, ethanol (EtOH), water (0.001 M oxalic acid catalyst) was kept constant at 1:5:7 respectively, while the molar ratio of TMES/TEOS (A) was varied from 0 to 0.6. It has been observed that as the A value increases, the gelation time increases. The hydrophobicity was tested by measuring the contact angle, and the surface chemical modification was confirmed by the FTIR spectroscopy studies. The thermal stability of the hydrophobic aerogels was studied in the temperature range from 25 to 800°C. The hydrophobic nature of the aerogel could be maintained up to a temperature of 287°C and above this temperature the aerogels become hydrophilic. The bulk density and the optical transmittance of the aerogels have been found to decrease with increase in A value. The aerogels have been characterized by Fourier transform infrared spectroscopy (FTIR), Optical transmittance, Scanning electron microscopy (SEM), Differential thermal analysis (DTA) and Thermogravimetric analysis (TGA), and Contact angle measurements.

35 citations


Journal ArticleDOI
TL;DR: In this article, several nitrate containing anionic clays were synthesized at different temperatures and the kinetics of NO3− release were determined to test their suitability as slow-release N fertilizers.
Abstract: Several nitrate containing anionic clays were synthesized at different temperatures and the kinetics of NO3− release were determined to test their suitability as slow-release N fertilizers. A sample (Mg:Al = 2:1) synthesized at 60°C with smaller particle size released 75, 86 and 100% of its NO3− in 1, 3 and 7 days, respectively when equilibrated with a simulated soil solution. On the other hand, the 175°C/2 hrs sample with larger particle size released 65, 77 and 84% of its nitrate in 1, 3 and 7 days, respectively. Another anionic clay (synthesized at 175°C/24 hrs) of higher charge density (Mg:Al = 2:1) containing NO3− was equilibrated with a 0.012 N NaCl or Na2CO3 to test the role of different anions in releasing the NO3− anion from the interlayers. The results showed that Cl− released more NO3− than did CO32− from this anionic clay after all the treatment times probably as a result of the CO32− anion blocking the release of NO3− from the interior of the crystals. When a lower charge density (Mg:Al = 3:1) sample (synthesized at 175°C/48 hrs) was equilibrated with 0.02N solution of anions the release of nitrate was as follows: Cl− < F− < SO4= ≤ CO32−. These results suggest that the divalent SO4= and CO32− anions are more effective in the release of NO3− from this lower charge density anionic clay. Time-resolved structural analysis of NO3− exchange with CO32− in the above anionic clay using synchrotron x-ray diffraction showed that ion exchange is rapid because of small crystal size and lower charge density. Thus the release of NO3− from anionic clays is an interplay among the type of anions present in soil solution, their concentration, pH of soil solution, the charge density and crystal size of anionic clay etc.

34 citations


Journal ArticleDOI
TL;DR: In this paper, the best operating conditions for optimum flux of water, which penetrates through the membrane and rejection (prevention of oil droplets from passing though the membrane) were obtained.
Abstract: Hydrophilic polyvinylidenefluoride (PVDF) membranes were employed for emulsified oil wastewater treatment The best operating conditions for optimum flux of water, which penetrates through the membrane and rejection (prevention of oil droplets from passing though the membrane) were obtained Concentration and pH effects on flux and rejection were determined Increase of weight concentration caused flux decline due to the formation of a thick layer on the membrane surface However increasing the concentration increased rejection The pH effects were complex By increasing the acidity of the feed, rejection was reduced

31 citations


Journal ArticleDOI
TL;DR: In this article, Zn-Al-Sn-CO3 was synthesized with di-, tri-and tetra-valent cations and reacted with organic monocarboxylic, dicarboxyl and aromatic acids at 60°C.
Abstract: Layered double hydroxide (LDH) is synthesized conventionally only with divalent and trivalent cations. In this study, Zn-Sn LDH consisting of di- and tetra-valent cations and Zn-Al-Sn LDH consisting of di-, tri- and tetra-valent cations were prepared and reacted with organic monocarboxylic, dicarboxylic and aromatic acids at 60°C. The 003 spacing of the prepared LDH (Zn-Sn-CO3) is 0.67 nm which is smaller compared to that of the usual LDH (Zn-Al-CO3) with 0.76 nm in the case of carbonate anion as the guest. Zn-Al-Sn-CO3 LDH has two 003 spacings i.e., 0.67 and 0.75 nm which belong to Zn-Sn-CO3 and Zn-Al-CO3 LDH, respectively. Analysis by DTA, TG and DTG indicated that the electrostatic force between the Zn-Sn layers and carbonate anions is larger than that of Zn-Al LDH. The carbonate anions in Zn-Sn LDH decomposed at 261°C while in the usual LDH they decomposed at 230–240°C.

26 citations


Journal ArticleDOI
TL;DR: In this paper, the effectiveness of microwave heating in an activation treatment of zeolites was studied and the utilization of X zeolite for reusable desiccant was examined and a degradation degree of adsorptive capacity for water was examined after three treatments.
Abstract: Effectiveness of microwave heating in an activation treatment of zeolites was studied and utilization of zeolites for reusable desiccant was examined. X zeolite was chosen as a target material for its large adsorption capacity. Na-X zeolite easily caused a thermal runaway by microwave radiation of 500 W but Ca contained X zeolite merely reached ca. 573 K under the same conditions. Mixtures of Na-X and Ca-X with suitably mixed ratios did not cause the thermal runaway and their heating temperatures were controlled (>573 K) at will. Under the most suitable conditions, the mixture reached a dehydration degree of 92%. A degradation degree of adsorptive capacity of the mixture for water was examined after three treatments. The average degradation degree was 1.5% per treatment. The heating method is promising as a quick and easy technique to activate zeolite. By applying the method, the zeolites with suitable mixing ratios are usable as a reusable desiccant for home use.

26 citations


Journal ArticleDOI
TL;DR: In this paper, Zr-pillared clays were prepared from ZrOCl2 pillaring solutions by adopting different preparative conditions and the resulting samples were characterized by XRD, TGA, N2 sorption and UV-VIS-Diffuse reflectance spectroscopy techniques.
Abstract: Zr-pillared clays were prepared from ZrOCl2 pillaring solutions by adopting different preparative conditions. Ce3+ ions are introduced to Zr-pillared clays by co-intercalation method. The resulting samples were characterized by XRD, TGA, N2 sorption and UV-VIS-Diffuse reflectance spectroscopy techniques. Basal spacings in the range of 18–21 A were observed depending upon the preparative condition. TG analysis shows three weight loss regions corresponding to removal of various types of water molecules. All pillared clays show Type-I sorption isotherm typical of microporous materials. Pillaring under refluxing condition is found to have beneficial effect on the surface area and pore volume of the Zr-pillared clay. The chemical environment and location of Ce3+ ions is studied by UV-VIS-DRS. The Ce3+ ions are found to be present in the micropores of the Zr-pillared clays. However heat treatment at higher temperature may result in peripheral interaction between Ce3+ ions and Zr-pillars. Catalytic activity of these pillared clays was evaluated for cyclohexanol dehydration which correlates well with the Bronsted acidity of these materials. The Zr-Pillared clay containing Ce3+ ions show good catalytic activity and stability with reaction time which has been ascribed to the stabilazition of the Bronsted acidic centers.

Journal ArticleDOI
TL;DR: In this article, a stochastic model was developed to predict the fraction of entrapped NaCl in the sintering and dissolution process (SDP) based on the assumption that the particles of the Al and NaCl powders used in SDP are spherical and monosized and that they are distributed randomly in the preform.
Abstract: The sintering and dissolution process (SDP) is a novel method for manufacturing Al foams. One concern of the process is the presence of residual NaCl in the as manufactured Al foams under certain circumstances, which may have undesirable effects on the properties of the foams. This paper develops a stochastic model to predict the fraction of entrapped NaCl based on the assumptions that the particles of the Al and NaCl powders used in SDP are spherical and monosized and that they are distributed randomly in the preform. The model predicts that the fraction of entrapped NaCl in the foam decreases with increasing volume fraction of NaCl in the preform and with decreasing NaCl-to-Al particle size ratio. The model predictions are in general agreements with the preliminary experimental measurements. The model provides a basis for the selection of Al and NaCl powders in order to minimise the entrapped NaCl in the foam.

Journal ArticleDOI
TL;DR: In this article, the effect of sintering temperature on porous silica composite strength was studied by discussing three factors, namely crystal phase, glassy phase and porosity, and found that up to 1360°C, the crystalline silica decreased gradually and the disappearing silica dissolved into the glass and became a part of glass network and resulted in the enhancement of glass strength.
Abstract: The effect of sintering temperature on porous silica composite strength was studied by discussing three factors, namely crystal phase, glassy phase and porosity. The fired products of clay and silica are composed of crystalline phase and glassy phase. The crystalline phases consist of alpha-quartz and mullite and the glassy phase contains a disordered silica network. With the increase of sintering temperature up to 1360°C, the crystalline silica decreased gradually. The disappearing silica dissolved into the glass and became a part of glass network and resulted in the enhancement of glass strength. This change in glass played an important role in the improvement of sample strength. At the same time, the increase of sintering temperature promoted the densification of samples and reduced the porosity of products, which also contribute to the increase of sample strength. When the sintering temperature is up to 1390°C, the silica in glass tended to convert to cristobalite with the expansion of glassy phase. This expansion weakened the connection of atoms in glass network and brought some closed pores into products, which led to the decrease of sample strength.

Journal ArticleDOI
TL;DR: In this article, the porosity and morphologies of carbon aerogels were characterized by nitrogen adsorption, apparent density, He- pycnometer method, and transmission electronic microscopy (TEM).
Abstract: Carbon aerogels were prepared by sol-gel polymerization of phenolic novolak and furfural followed by supercritical drying and pyrolysis. The porosity and morphologies of carbon aerogels were characterized by nitrogen adsorption, apparent density, He- pycnometer method, and transmission electronic microscopy (TEM). Effect of ratios of phenolic novolak to furfural (Ra) and total concentration of reactants (C) in sol-gel step on porosity and morphologies of carbon aerogels was investigated. The carbon aerogels synthesized are rich in meso- and macropores. The Ra determines the cross-linking density of polymers, thereby the compatibility of the polymers, and ultimately the shrinkage of gels in the drying and pyrolysis. The network sizes and the porosity of organic and carbon aerogels are mainly determined by Ra. The C has no effect on volume shrinkage of gels in drying and pyrolysis and has only dilute effect in determining bulk density of organic and carbon aerogels, and ultimately the porosity of carbon aerogels. Conversion of mesopores to micro- and macropores is observed, which is related to combination of C and Ra, and determines the partition of micro-, meso- and macropores.

Journal ArticleDOI
TL;DR: In this paper, a computational code called OOF is adopted, which converts digitalized two-dimensional (2D) images of materials microstructures into finite element meshes, so that the effect of 2-D microstructural features (e.g. pore size and shape) on the global mechanical response of the material can be determined.
Abstract: Porous glass with closed controlled porosity is used as a model system in order to numerically assess the effect of pores on the macroscopic mechanical and fracture behavior of brittle solids. A computational code called OOF, which converts digitalized two-dimensional (2-D) images of materials microstructures into finite element meshes, is adopted, so that the effect of 2-D microstructural features (e.g. pore size and shape) on the global mechanical response of the material can be determined. Firstly, microstructures of porous glass bodies containing isolated pores were considered. These specimens were numerically investigated in terms of fracture initiation and propagation: the numerical model predicted that larger pores initiate fracture, in agreement with experimental results. Then, the effect of porosity on the elastic and fracture properties was thoroughly investigated by means of model two-dimensional microstructures consisting of selected area fractions of pores (equivalent to pore volume fractions in three dimensions) and with prescribed pore shape, orientation and dimensions. In particular, the effect of pore dimension and shape was studied, finding that the critical stress for crack initiation scales with pore dimension and aspect ratio, i.e. oblate and larger pores oriented perpendicularly to the stress direction cause a higher reduction of strength of the specimen. Finally, several 2-D microstructures characterized by different values of area fraction of pores of the same shape were investigated, in order to determine the variation of elastic properties and the fracture response of porous glasses with pore content. The study confirms the suitability of the 2-D OOF code to investigate the mechanical and fracture behavior of porous materials. Issues regarding the limitation of the model due to its 2-D character are also discussed where appropriate.

Journal ArticleDOI
TL;DR: In this paper, the nitrogen adsorption data described in the following paper gives a pore size for both the macropore cavity and the mesopore openings leading into the cavity.
Abstract: Three-dimensionally ordered silica structures containing both mesopores and macropores are created using polystyrene coacervate spheres with a diameter of ca. 146 nm. The close-packed polystyrene coacervate spheres are intercalated with tetraethyl orthosilicate. The spheres are removed by calcination leaving an inverse silica replica with a spherical macropore cavity diameter of ∼110 nm. Due to the nature of these porous structures, pores leading into the macropore cavity are in the mesopore regime, ∼40 nm in diameter. The nitrogen adsorption data described in the following paper gives a pore size for both the macropore cavity and the mesopore openings leading into the cavity. The pore sizes as determined by nitrogen sorption are in good agreement with the pore sizes observed by scanning electron microscopy. Mercury intrusion porosimetry results confirm the size of the mesopore openings leading into the macropore cavity, however due to destruction of the sample upon intrusion, extrusion results can not be obtained to determine main cavity diameters. As a result, nitrogen sorption may be a viable option for determining pore sizes with these three-dimensionally ordered materials containing both mesopores and macropores.

Journal ArticleDOI
TL;DR: In this paper, 2,2,azobis-2-methylpropionitrile (AIBN) in the presence of dodecanol was used as a porogen agent and radical polymerization was carried out using an in situ prepared Mg(OH)2 gel.
Abstract: 2-Hydroxyethyl methacrylate (HEMA), methyl methacrylate (MMA) monomers and ethyleneglycol dimethacrylate (EDMA) as a cross-linker, were reacted with the initiator 2,2,azobis-2-methylpropionitrile (AIBN) in the presence of dodecanol The effect of increasing concentrations of dodecanol, as a porogen agent, was evaluated The radical polymerization was carried out using an in situ prepared Mg(OH)2 gel, at 70°C for 5 h Following polymerization, the suspension was eliminated by neutralization for recovery of beads The spherical particles obtained were filtered, washed with methanol using simple extraction and using a Soxhlet thimble, and dried at 60°C under vacuum Scanning Electron Microscopy (SEM) revealed regularly shaped spherical beads containing macropores Nitrogen Sorption Analysis (NSA) and Mercury Intrusion Porosimetry (MIP) were performed for evaluation of surface area, pore size and pore volume

Journal ArticleDOI
TL;DR: In this article, ZSM-5 and mordenite were synthesized directly using poly(ethylene glycol) (PEG 200) as a structure-directing agent.
Abstract: ZSM-5 (SiO2/Al2O3 = 55) and mordenite (SiO2/Al2O3 = 48) were synthesized directly using poly(ethylene glycol) (PEG 200) as a structure-directing agent. The PEG 200 molecules were occluded in the pores of ZSM-5 but not in mordenite. It is expected that the formation of ZSM-5 occurs via a layered phase such as magadiite.

Journal ArticleDOI
TL;DR: The synthesis of super-microporous aluminosilicate with a pore diameter of 146 A has been achieved by means of synthesis under specified conditions with a skeletal material comprising TMOS and a small quantity of sodium aluminate, and a conventional alkyl-trimethylammonium halide (C10TMABr) as a template as discussed by the authors.
Abstract: The synthesis of super-microporous aluminosilicate with a pore diameter of 146 A has been achieved, by means of synthesis under specified conditions with a skeletal material comprising TMOS and a small quantity of sodium aluminate, and a conventional alkyl-trimethylammonium halide (C10TMABr) as a template This super-microporous aluminosilicate has an adsorption capacity of 02 ml/g at a relative water vapor pressure of 02, and thus is promising as an adsorbent for an adsorption heat-pump

Journal ArticleDOI
TL;DR: In this article, the synthesis of mesoporous aluminosilicates from a hybrid organic-inorganic xerogel, using the chitosan biopolymer together with a hydrothermal treatment process as structural modeling tools, is presented.
Abstract: This paper presents the synthesis of mesoporous aluminosilicates from a hybrid organic-inorganic xerogel, using the chitosan biopolymer together with a hydrothermal treatment process as structural modeling tools. The properties of the material obtained point to an important role of the chitosan as a stabilizer of the structural lattice.

Journal ArticleDOI
TL;DR: In this paper, a comparison between the micropore size distributions was performed using the Medek model, and it was concluded that the catalysts block part of the initial microporous structure, leading to a decrease in micropores volume and to an increase of the mean equivalent radius.
Abstract: Impregnated active carbons were prepared to be used as catalysts of complete oxidation, aiming the reduction of atmospheric emission of volatile organic compounds. The onversion efficiency is regulated by the catalyst dispersion in the porous structure where pollutants can access to be converted, which means that a good dispersion is required. Therefore, microporore size distribution has an important role on the catalyst efficiency, either because the access to the catalyst can be made through micropores, or because micropores can offer a significant deposition surface, if they are wide enough. When the impregnation is performed on the raw material or after activation, the micropore size distribution is already well studied. This paper aims to analyse that distribution when impregnation is performed after carbonization, because this knowledge is yet very scarce. Nut and almond shells were used as raw materials to prepare carbons impregnated with CoO and Co3O4. The comparison between the micropore size distributions was performed using Medek model. When impregnation is made after activation, it was concluded that, for both raw materials, the catalysts block part of the initial microporous structure, leading to a decrease in micropore volume and to an increase of the mean equivalent radius. When impregnation step is conducted after carbonization, the total micropore volume can increase or decrease in relation to the non-impregnated carbons, depending on the catalyst distribution and type of carbonized support. Nevertheless, all the carbons analysed showed that impregnation after carbonization increases micropore volume of wider micropores.

Journal ArticleDOI
Pingchuan Sun1, Qinghua Jin1, Lijun Wang1, Baohui Li1, Datong Ding1 
TL;DR: In this paper, computer simulation of the interactions of diquaternary cations with zeolites was carried out to determine the templating ability of DICs in the formation of these zeolite.
Abstract: Computer simulation of the interactions of diquaternary cations with zeolites ZSM-50, NU-87, ZSM-23 and ZSM-12 is carried out to determine the templating ability of diquaternary cations in the formation of these zeolites. The calculated energies are a measure of “match” between the geometry of diquaternary cations and the topology of the zeolite framework. The systematic synthesis results of Mioni et al., especially the dependence of the products on the chain lengths of diquaternary cations are rationalized quantitatively. We infer that it is consistent with the templating theory of zeolite synthesis that ZSM-12 and ZSM-23 both can be formed by more than one type of diquaternary cations.

Journal ArticleDOI
TL;DR: In this paper, small-angle scattering experiments in combination with scanning electron microscopy have been performed to determine the texture properties of a selected mesoporous glass and a well-defined range order L ≈ 60 nm has been selected.
Abstract: Nitrogen adsorption, mercury intrusion, scanning electron microscopy and small-angle X-ray scattering have been used to determine the texture properties of a selected mesoporous glass The glass has been prepared by a combined acid and alkaline leaching treatment of a phase separated sodium-borosilicate initial glass Residues of silica gel, remaining in the pores of the investigated glass after the treatment with alkaline solution, lead to differences in the results of the standard characterization techniques nitrogen adsorption and mercury intrusion In order to explain these differences, small-angle scattering experiments in combination with scanning electron microscopy have been performed Here, a well-defined range order L ≈ 60 nm has been selected and a 50% porosity results The behaviour of the second derivative of the small-angle scattering correlation function has been checked by the use of the linear simulation model

Journal ArticleDOI
TL;DR: In this paper, the absorption efficiency of dehydrated Na12 − 2xCa x -A zeolites with x = 0, 1.1 and 4 in microwave heating were experimentally and theoretically investigated and compared with one another.
Abstract: Properties of dehydrated Na12 − 2xCa x -A zeolites with x = 0, 1.1 and 4 in microwave heating were experimentally and theoretically investigated and compared with one another. Final heating temperatures of zeolites by microwave radiation were measured against radiation time and the easiness of heating was in the order of Na12-A ≫ Na10Ca1-A > Na4Ca4-A for every irradiating condition studied. Microwave (relative) absorption efficiencies of the zeolites were calculated as a function of temperature with a simple method by using dielectric properties of the dehydrated states. In every temperature calculated, the order of absorption efficiency was Na12-A ≫ Na10Ca1-A ≈ Na4Ca4-A. From these results, it was clearly verified that Na+ ion on the site III played the most important role in absorbing microwaves because Na12-A has one Na+ ion on the site III but Na10Ca1-A and Na4Ca4-A have no cations on the site.

Journal ArticleDOI
TL;DR: In this article, the effect of corn-starch on positive temperature coefficient of resistivity (PTCR) characteristics and microstructures of Sb-doped BaTiO3 ceramics was investigated.
Abstract: Sb-doped BaTiO3 ceramics containing corn-starch were prepared by sintering at 1350°C for 1 h in air. In this study, the effect of corn-starch on positive temperature coefficient of resistivity (PTCR) characteristics and microstructures of Sb-doped BaTiO3 ceramics was investigated. It was found that the porosity and pore size increased and the grain size slightly decreased with increasing corn-starch content. XRD results showed the presence of BaTiO3 peaks only in the Sb-doped BaTiO3 ceramics with and without corn-starch. The PTCR jump of the Sb-doped BaTiO3 ceramics with corn-starch was over 106 and 1–2 orders higher than that of samples without corn-starch. The increase in the room-temperature resistivity with increasing corn-starch content was attributed mainly to the increase in the electrical barrier height of grain boundaries and the porosity as well as the partial decrease in the donor concentration of grains and the grain size. It was also noticed that the grain boundary resistivity contributed largely to the total resistivity of the Sb-doped BaTiO3—corn-starch ceramics.

Journal ArticleDOI
TL;DR: In this article, an experimental strategy was developed to obtain Si-Al-Zr transparent sols via the sol-gel process, which was prepared from Al(OBus)3 (OBus: C2H5CH(CH3)O), Zr(OPrn)4 (OPrn: OCH2CH2Ch3) and Si(OEt)4.
Abstract: An experimental strategy was developed to obtain Si—Al—Zr transparent sols via the sol-gel process. The sol was prepared from Al(OBus)3 (OBus: C2H5CH(CH3)O), Zr(OPrn)4 (OPrn: OCH2CH2CH3) and Si(OEt)4. The chelating agents acetylacetone (2, 4 pentanedione, acacH), and itaconic anhydride (2-methylenesuccinic anhydride, anhH) were employed separately to stabilize Al and Zr precursors in order to control their chemical reactivity, avoiding precipitation. In all cases a prehydrolyzed tetraethyl orthosilicate (TEOS) sol was the Si source. We use the Partial Charge Model as a theoretical indication of the stabilization of the Al and Zr species derived from the reaction with anhH and acacH. The sols were polymerized at room temperature (293 K) to obtain gels and these were dried and calcined at 673, 773 and 873 K in air. The characterization techniques were Small Angle X-ray Scattering (SAXS), Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Thermal Gravimetric (TGA) and Differential Thermal Analyses (DTA). The porosity and surface area of solids calcined at 673, 773 and 873 K were determined by N2 adsorption/desorption isotherms. The corresponding average pore diameter was evaluated using the methods BJH, HK and DA. These models were used because all together cover the full range of the pore size.